Thin-layer-covered multilayer golf ball

ABSTRACT

A golf ball includes a core formed of an inner core and at least one outer core layer disposed about the inner core, one of which includes a surface amount of trans-polybutadiene and an interior amount of trans-polybutadiene at least 6 percent less than the surface amount. A cover containing an inner cover layer and an outer cover layer is formed over the core. The inner cover layer includes a block copolymer of styrene and butadiene, isoprene, or ethylene-butylene rubber and has a material hardness of about 60 to 70 Shore D. The outer cover layer is formed from a castable polyurethane or polyurea and having a material hardness of 55 Shore D or less. The inner core has an interior hardness and a surface hardness differing from the interior hardness by greater than 20 percent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/421,956, filed Jun. 2, 2006, which is a continuation ofco-pending U.S. patent application Ser. No. 10/956,329, filed Oct. 1,2004 and now abandoned, which is a continuation of co-pending U.S. Pat.No. 6,913,547, filed Feb. 13, 2001, which is a continuation-in-part ofU.S. Pat. No. 7,090,798, filed Mar. 22, 1999, which is acontinuation-in-part of U.S. Pat. No. 5,885,172; and also acontinuation-in-part of U.S. Pat. No. 6,486,261, filed Nov. 27, 2000,which is a continuation-in-part of U.S. Pat. No. 6,210,294, filed May14, 1999, and U.S. Pat. No. 6,465,578, filed Dec. 16, 1999, each ofwhich is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

This invention relates generally to golf balls, and more specifically,to multilayer golf balls. In particular, this invention relates to agolf ball having a core comprising a center and an outer core layer, anda cover comprising an inner cover layer and a thin outer cover layer.The outer cover layer is formed of a thermoset material formed from acastable, reactive liquid. The core is formed of a polybutadienecomposition comprising a butadiene polymer with a resilience indexgreater than about 40 and a molecular weight greater than about 200,000.

BACKGROUND OF THE INVENTION

Conventional golf balls can be divided into several general classes: (a)solid golf balls having one or more layers, and (b) wound golf balls.Solid golf balls include one-piece balls, which are easy to constructand relatively inexpensive, but have poor playing characteristics andare thus generally limited for use as range balls. Two-piece balls areconstructed with a generally solid core and a cover and are generallythe most popular with recreational golfers because they are very durableand provide maximum distance. Typically, the core is formed frompolybutadiene that is chemically crosslinked with zinc diacrylate and/orother similar crosslinking agents. These balls are generally easy tomanufacture, but are regarded as having limited playing characteristics.Solid golf balls also include multi-layer golf balls that are comprisedof a solid core of one or more layers and/or a cover of one or morelayers. These balls are regarded as having an extended range of playingcharacteristics.

Wound golf balls are generally preferred by many players due to theirhigh spin and soft “feel” characteristics. Wound golf balls typicallyinclude a solid, hollow, or fluid-filled center, surrounded by atensioned elastomeric material, and a cover. Wound balls generally aremore difficult and expensive to manufacture than solid two-piece balls.

A variety of golf balls have been designed by manufacturers to provide awide range of playing characteristics, such as compression, velocity,“feel,” and spin. These characteristics can be optimized for variousplaying abilities. For example, one component that manufacturerscommonly alter to change the playing characteristics of golf balls isthe polymer composition used to form golf ball centers and/or cores. Oneof the most common polymers employed is polybutadiene and, morespecifically, polybutadiene having a high cis-isomer concentration.

The use of a polybutadiene having a high cis-concentration results in avery resilient and rigid golf ball, especially when coupled with a hardcover material. These highly resilient golf balls have a relatively hard“feel” when struck by a club. Soft “feel” golf balls constructed with ahigh cis-polybutadiene have low resilience. In an effort to provideimproved golf balls, various other polybutadiene formulations have beenprepared, as discussed below.

U.S. Pat. No. 3,239,228 discloses a solid golf ball having a core moldedof polybutadiene rubber with a high sulfur content, and a cover. Thepolybutadiene content of the core is stereo-controlled to theconfiguration 25-100 percent cis- and 0-65 percenttrans-1,4-polybutadiene, with any remainder having a vinyl configurationof polybutadiene. A preferred embodiment of the polybutadiene golf ballcore contains 35 percent cis-, 52 percent trans-, and 13 percentvinyl-polybutadiene. The level of trans- and vinyl-content are disclosedto be unimportant to the overall playing characteristics of the polymerblend.

British Patent No. 1,168,609 discloses a molding composition from whichimproved golf ball cores can be molded and which containscis-polybutadiene as a basic polymer component. The core polymercomponent typically includes at least 60 percent cis-polybutadiene, withthe remainder being either the trans- or vinyl-forms of polybutadiene.In a preferred embodiment, the core polybutadiene component contains 90percent cis-configuration, with the remaining 10 percent being eitherthe trans- or vinyl-configurations of 1,4-polybutadiene.

U.S. Pat. Nos. 3,572,721 and 3,572,722 disclose a solid, one- ortwo-piece golf ball, with the two-piece ball having a core and a cover.The cover material can include any one of a number of materials, orblends thereof, known to those of ordinary skill in the art, includingtrans-polybutadiene which may be present in an amount from at least 90percent, with the remainder being the cis- and/or vinyl configuration.

British Patent No. 1,209,032 discloses a two- or three-piece golf ballhaving a core and a cover. The core or cover material can be anymaterial capable of being crosslinked. In particular, the material canbe a polymer or a copolymer of butadiene or isoprene. Preferably, thepolymer component is polybutadiene having a cis content of greater than50 percent by weight.

U.S. Pat. No. 3,992,014 discloses a one-piece, solid golf ball. The golfball material is typically polybutadiene, with a stereo-configurationselected to be at least 60 percent cis-polybutadiene, with the remaining40 percent being the trans-polybutadiene and/or 1,2-polybutadiene(vinyl) isomers.

U.S. Pat. No. 4,692,497 discloses a golf ball and material thereofformed by curing a diene polymer including polybutadiene and a metalsalt of an alpha, beta ethylenically unsaturated acid using at least twofree radical initiators.

U.S. Pat. No. 4,931,376 discloses a process for producing butadienepolymers for use in various applications, including golf ball covermaterials. One embodiment of the invention employs a blended polymericresin material, including at least 30 percent by weight of atrans-polybutadiene polymer as a golf ball cover on a two-piece ball. Ina preferred embodiment, the golf ball cover material contains a blendincluding 30 to 90 percent by weight of a trans-polybutadiene polymer.

U.S. Pat. No. 4,971,329 discloses a solid golf ball made from apolybutadiene admixture of cis-1,4 polybutadiene and 1,2 polybutadiene,a metal salt of an unsaturated carboxylic acid, an inorganic filler, anda free radical initiator. The admixture has about 99.5 percent to about95 percent by weight of cis-1,4 polybutadiene and about 0.5 percent toabout 5 percent by weight of 1,2 polybutadiene.

U.S. Pat. No. 5,252,652 discloses a one-piece or multi-layered golf ballcore with improved flying performance from a rubber compositioncomprising a base rubber, preferably 1,4-polybutadiene with acis-content of at least 40 mole percent, an unsaturated carboxylic acidmetal salt, an organic peroxide, and an organic sulfur compound and/or ametal salt thereof. The organic sulfur compound and/or a metal salt istypically present in an amount from about 0.05 to 2 parts per hundred byweight and the organic peroxide is typically present in an amount fromabout 0.5 to 3 parts per hundred by weight of the total polymercomponent.

European Patent No. 0 577 058 discloses a golf ball containing a coreand a cover that is formed as two separate layers. The inner layer ofthe cover is molded over the core and is formed from ionomer resin. Theouter layer of the cover is molded over the inner layer and is formedfrom a blend of natural or synthetic balata and a crosslinkableelastomer, such as polybutadiene. In one embodiment of the outer layerof the cover, the elastomer is 1,4-polybutadiene having a cis-structureof at least 40 percent, with the remaining 60 percent being thetrans-isomer. A preferred embodiment contains a cis-structure of atleast 90 percent and more preferably, a cis-structure of at least 95percent.

U.S. Pat. No. 5,421,580 discloses a wound golf ball having a liquidcenter contained in a center bag, a rubber thread layer formed on theliquid center, and a cover over the wound layer and liquid center. Thecover material can include any one of a number of materials, or blendsthereof, known to those of ordinary skill in the art, includingtrans-polybutadiene and/or 1,2-polybutadiene (vinyl), such that thecover has a JIS-C hardness of 70-85; preferred trans-percentages are notdisclosed.

U.S. Pat. No. 5,697,856 discloses a solid golf ball having a core and acover wherein the core is produced by vulcanizing a base rubbercomposition containing a butadiene rubber having a cis-polybutadienestructure content of not less than 90 percent before vulcanization. Theamount of trans-polybutadiene structure present after vulcanization is10 to 30 percent, as amounts over 30 percent are alleged todetrimentally result in cores that are too soft with deterioratedresilience performance, and to cause a decrease in golf ballperformance. The core includes a vulcanizing agent, a filler, an organicperoxide, and an organosulfur compound.

British Patent No. 2,321,021 discloses a solid golf ball having a coreand a cover formed on the core and having a two-layered coverconstruction having an inner cover layer and an outer cover layer. Theouter cover layer is comprised of a rubber composite that contains 0.05to 5 parts by weight of an organic sulfide compound. The core rubbercomposition comprises a base rubber, preferably 1,4-polybutadiene havinga cis-content of at least 40 percent by weight, a crosslinking agent, aco-crosslinking agent, an organic sulfide, and a filler. Thecrosslinking agent is typically an organic peroxide present in an amountfrom 0.3 to 5.0 parts by weight and the co-crosslinking agent istypically a metal salt of an unsaturated fatty acid present in an amountfrom 10 to 40 parts by weight. The organic sulfide compound is typicallypresent from 0.05 to 5 parts by weight.

U.S. Pat. No. 5,816,944 discloses a solid golf ball having a core and acover wherein the core has a JIS-C hardness of 50 to 80 and the coverhas a Shore-D hardness of 50 to 60. The core material includesvulcanized rubber, such as cis-polybutadiene, with a crosslinker, anorganic peroxide, an organosulfur compound and/or a metal-containingorganosulfur compound, and a filler.

Additionally, conventional polymers that have a high percentage of thetrans-polybutadiene conformation, such as DIENE 35NF, from FirestoneCorp., that has 40 percent cis-isomer and 50 percent trans-polybutadieneisomer, and mixtures of high-cis- and high-trans-polybutadiene isomers,such as CARIFLEX BR1220, from Shell Corporation, and FUREN 88, fromAsahi Chemical Co., respectively, typically do not yield high resiliencevalues and therefore are not desirable.

In addition to changing center or core ingredients to affect golf ballperformance characteristics, a number of patents have issued that aredirected towards modifying the properties of layers and covers used informing a variety of golf balls, such as wound balls, conventional solidballs, multi-layer balls having dual cover layers, dual core layers,and/or balls having a mantle layer disposed between the cover and thecore. The most common polymers used by manufacturers in golf ball layersand covers have been ionomers, such as SURLYN, commercially availablefrom E.I. DuPont de Nemours and Co., of Wilmington, Del. Recently,however, manufacturers have investigated the used of alternativepolymers, such as polyurethane. For example, U.S. Pat. No. 3,147,324 isdirected to a method of making a golf ball having a polyurethane cover.

Polyurethanes have been recognized as useful materials for golf ballcovers since about 1960. Polyurethane is the product of a reactionbetween a polyurethane prepolymer and a curing agent. The polyurethaneprepolymer is a product formed by a reaction between a polyol and adiisocyanate. The curing agents used previously are typically diaminesor glycols. A catalyst is often employed to promote the reaction betweenthe curing agent and the polyurethane prepolymer.

Since 1960, various companies have investigated the usefulness ofpolyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061teaches a golf ball made from a polyurethane prepolymer of polyether anda curing agent, such as a trifunctional polyol, a tetrafunctionalpolyol, or a diamine. U.S. Pat. No. 5,334,673 discloses the use of twocategories of polyurethane available on the market, i.e., thermoset andthermoplastic polyurethanes, for forming golf ball covers and, inparticular, thermoset polyurethane covered golf balls made from acomposition of polyurethane prepolymer and a slow-reacting amine curingagent, and/or a difunctional glycol. The first commercially successfulpolyurethane covered golf ball was the Titleist® Professional ball,first released in 1993.

Unlike SURLYN® or ionomer-covered golf balls, polyurethane golf ballcovers can be formulated to possess the soft “feel” of balata coveredgolf balls. However, golf ball covers made from polyurethane have not,to date, fully matched SURLYN®-covered golf balls with respect toresilience or the rebound that is a function of the initial velocity ofa golf ball after impact with a golf club.

U.S. Pat. No. 3,989,568 discloses a three-component system employingeither one or two polyurethane prepolymers and one or two polyols orfast-reacting diamine curing agents. The reactants chosen for the systemmust have different rates of reactions within two or more competingreactions.

U.S. Pat. No. 4,123,061 discloses a golf ball made from a polyurethaneprepolymer of polyether and a curing agent, such as a trifunctionalpolyol, a tetrafunctional polyol, or a fast-reacting diamine curingagent.

U.S. Pat. No. 5,334,673 discloses a golf ball cover made from acomposition of a polyurethane prepolymer and a slow-reacting polyaminecuring agent and/or a difunctional glycol. Resultant golf balls arefound to have improved shear resistance and cut resistance compared tocovers made from balata or SURLYN®.

U.S. Pat. No. 5,692,974 discloses methods of using cationic ionomers ingolf ball cover compositions. Additionally, the patent relates to golfballs having covers and cores incorporating urethane ionomers. Improvedresiliency and initial velocity are achieved by the addition of analkylating agent such as t-butyl-chloride which induces ionicinteractions in the polyurethane to produce cationic type ionomers.

International Patent Application WO 98/37929 discloses a composition forgolf ball covers that comprises a blend of a diisocyanate/polyolprepolymer and a curing agent comprising a blend of a slow-reactingdiamine and a fast-reacting diamine. Improved “feel,” playability, anddurability characteristics are exhibited.

Conventional polyurethane elastomers are known to have lower resiliencythan SURLYN® and other ionomer resins. It has now been discovered thatthe use of a polyurethane composition, according to the presentinvention, in forming golf ball cores, intermediate and mantle layers,and/or covers, can raise the velocity of a golf ball prepared with thecomposition: (1) closer to the velocities observed with SURLYN®-coveredgolf balls; and (2) higher than the velocities exhibited usingalternative urethane compositions. Additionally, it is desired tocombine polyurethane cover compositions with polybutadiene corematerials, especially those having resilience indices greater than about40. Cores formed of materials such as these have been found to provideexceptional resiliency characteristics without a loss in performancecharacteristics (i.e., decreased compression).

A multi-layered core construction facilitates the ability to modify aball's moment of inertia through the manipulation of the specificgravity of each individual core layer. By using a multi-layered coreconstruction, a ball designer is able to control a ball's spinperformance when hit with full shots. With full shots, the ball's innerconstruction greatly affects the ball's spin rate. Thus, the spin rateof driver and long iron shots can be controlled more precisely throughuse of multi-layer core technology. Further, the ball's feel can beinfluenced with greater control than can be achieved from a single solidcore construction by modifying the hardness or compressibility of theindividual layers.

Therefore, it is thus desired to prepare multi-layered golf balls havinglower compression, while having the same or higher resilience thanconventional balls. It is alternatively desired to obtain the same orlower compression while achieving greater resilience, both withoutundesirable decrease in velocity.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball comprising a core and acover disposed about the core, wherein the core comprises a center andat least one outer core layer adjacent the center, and the covercomprises at least one inner cover layer and an outer cover layer;wherein the center has an outer diameter from about 0.375 in to about1.4 in and deflection of greater than about 4.5 mm under a load of 100Kg; the outer core layer has an outer diameter of from about 1.4 in toabout 1.62 in; the inner cover layer has an outer diameter of greaterthan about 1.58 in and a material hardness of less than about 72 ShoreD; and the outer cover layer has a hardness of greater than about 50Shore D.

In one embodiment, the outer cover layer has a material hardness lessthan about 55 shore D and, preferably, the outer cover layer has amaterial hardness less than about 50 shore D. The inner cover layershould have a material hardness between about 60 and about 70 Shore Dand, more preferably, between about 60 and about 65 Shore D.

In another embodiment, the inner cover layer outer diameter is fromabout 1.59 in to about 1.66 in and, more preferably, from about 1.6 into about 1.64 in. The center outer diameter should be from about 0.5 into about 1.25 in and, more preferably, from about 0.9 in to about 1.2in. The outer core layer outer diameter should be from about 1.52 in toabout 1.59 in and, more preferably, from about 1.535 in to about 1.58in.

In yet another embodiment, the ball has a moment of inertia of less thanabout 83 g·cm². Additionally, the center preferably has a firsthardness, the outer core layer has a second hardness greater than thefirst, and the inner cover layer has a third hardness greater than thesecond. In a preferred embodiment, the outer cover layer has a fourthhardness less than the third hardness.

In one embodiment, the center has a first specific gravity and the outercore layer has a second specific gravity that differ by less than about0.1. In a preferred embodiment, the center is solid. The center may alsobe liquid, hollow, or air-filled.

The present invention is also directed to a golf ball comprising a coreand a cover disposed about the core, wherein the core comprises a solidcenter and an outer core layer adjacent the center, and the covercomprises an inner cover layer and an outer cover layer; wherein thecenter has an outer diameter from about 0.375 in to about 1.4 in anddeflection of greater than about 4.5 mm under a load of 100 Kg; theouter core layer has an outer diameter of from about 1.4 in to about1.62 in; the inner cover layer has an outer diameter of greater thanabout 1.58 in and a material hardness of less than about 72 Shore D; andthe outer cover layer has a hardness of greater than about 50 Shore D.

In one embodiment, the outer cover layer has a material hardness of lessthan about 50 and a thickness of less than about 0.035 in. In apreferred embodiment, the center has a first hardness, the outer corelayer has a second hardness greater than the first, and the inner coverlayer has a third hardness greater than the second. Additionally, theouter cover layer has a fourth hardness less than the third hardness.

In another embodiment, the inner cover layer outer diameter is fromabout 1.59 in to about 1.66 in and, preferably, from about 1.6 in toabout 1.64 in. The center outer diameter should be from about 0.5 in toabout 1.25 in and, preferably, from about 0.9 in to about 1.2 in. In yetanother embodiment, the outer core layer outer diameter is from about1.52 in to about 1.59 in. Additionally, the ball can have a moment ofinertia of less than about 83 g·cm². In another embodiment, the centerhas a first specific gravity and the outer core layer has a secondspecific gravity that differ by less than about 0.1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball having a dual cover anda dual core according to the invention.

DEFINITIONS

The term “about,” as used herein in connection with one or more numbersor numerical ranges, should be understood to refer to all such numbers,including all numbers in a range.

As used herein, “cis-to-trans catalyst” means any component or acombination thereof that will convert at least a portion ofcis-polybutadiene isomer to trans-polybutadiene isomer at a giventemperature. It should be understood that the combination of thecis-isomer, the trans-isomer, and any vinyl-isomer, measured at anygiven time, comprises 100 percent of the polybutadiene.

As used herein, the term “active ingredients” is defined as the specificcomponents of a mixture or blend that are essential to the chemicalreaction.

As used herein, substituted and unsubstituted “aryl” groups means ahydrocarbon ring bearing a system of conjugated double bonds, typicallycomprising 4n+2π ring electrons, where n is an integer. Examples of arylgroups include, but are not limited to phenyl, naphthyl, anisyl, tolyl,xylenyl and the like. According to the present invention, aryl alsoincludes heteroaryl groups, e.g., pyrimidine or thiophene. These arylgroups may also be substituted with any number of a variety offunctional groups. In addition to the functional groups described hereinin connection with carbocyclic groups, functional groups on the arylgroups can include hydroxy and metal salts thereof; mercapto and metalsalts thereof; halogen; amino, nitro, cyano, and amido; carboxylincluding esters, acids, and metal salts thereof; silyl; acrylates andmetal salts thereof; sulfonyl or sulfonamide; and phosphates andphosphites; and a combination thereof.

As used herein, the term “Atti compression” is defined as the deflectionof an object or material relative to the deflection of a calibratedspring, as measured with an Atti Compression Gauge, that is commerciallyavailable from Atti Engineering Corp. of Union City, N.J. Atticompression is typically used to measure the compression of a golf ball.When the Atti Gauge is used to measure cores having a diameter of lessthan 1.680 in, it should be understood that a metallic or other suitableshim is used to make the diameter of the measured object 1.680 in. Asused herein, substituted and unsubstituted “carbocyclic” means cycliccarbon-containing compounds, including, but not limited to cyclopentyl,cyclohexyl, cycloheptyl, adamantyl, and the like. Such cyclic groups mayalso contain various substituents in which one or more hydrogen atomshas been replaced by a functional group. Such functional groups includethose described above, and lower alkyl groups having from 1-28 carbonatoms. The cyclic groups of the invention may further comprise aheteroatom.

As used herein, the term “coefficient of restitution” for golf balls isdefined as the ratio of the rebound velocity to the inbound velocitywhen balls are fired into a rigid plate. The inbound velocity isunderstood to be 125 ft/s.

As used herein, the terms “Group VIA component” or “Group VIA element”mean a component that includes a sulfur component, a selenium component,or a tellurium component, or a combination thereof.

As used herein, the term “sulfur component” means a component that iselemental sulfur, polymeric sulfur, or a combination thereof. It shouldbe further understood that “elemental sulfur” refers to the ringstructure of S8 and that “polymeric sulfur” is a structure including atleast one additional sulfur relative to the elemental sulfur.

As used herein, the term “fluid” includes a liquid, a paste, a gel, agas, or any combination thereof.

As used herein, the term “molecular weight” is defined as the absoluteweight average molecular weight. The molecular weight is determined bythe following method: approximately 20 mg of polymer is dissolved in 10mL of tetrahydrofuran (“THF”), which may take a few days at roomtemperature depending on the polymer's molecular weight anddistribution. One liter of THF is filtered and degassed before beingplaced in a high-performance liquid chromatography (“HPLC”) reservoir.The flow rate of the HPLC is set to 1 mL/min through a Viscogel column.This non-shedding, mixed bed, column model GMHHR-H, which has an ID of7.8 mm and 300 mm long is available from Viscotek Corp. of Houston, Tex.The THF flow rate is set to 1 mL/min for at least one hour before sampleanalysis is begun or until stable detector baselines are achieved.During this purging of the column and detector, the internal temperatureof the Viscotek TDA Model 300 triple detector should be set to 40° C.This detector is also available from Viscotek Corp. The three detectors(i.e., Refractive Index, Differential Pressure, and Light Scattering)and the column should be brought to thermal equilibrium, and thedetectors should be purged and zeroed, to prepare the system forcalibration according to the instructions provided with this equipment.A 100-μL aliquot of sample solution can then be injected into theequipment and the molecular weight of each sample can be calculated withthe Viscotek's triple detector software. When the molecular weight ofthe polybutadiene material is measured, a dn/dc of 0.130 should alwaysbe used. It should be understood that this equipment and these methodsprovide the molecular weight numbers described and claimed herein, andthat other equipment or methods will not necessarily provide equivalentvalues as used herein.

As used herein, the term “multilayer” means at least two layers andincludes liquid center balls, wound balls, hollow-center balls, andballs with at least two intermediate layers and/or an inner or outercover.

As used herein, the term “thermoset” material refers to an irreversible,solid polymer that is the product of the reaction of two or moreprepolymer precursor materials.

As used herein, the term “parts per hundred,” also known as “phr,” isdefined as the number of parts by weight of a particular componentpresent in a mixture, relative to 100 parts by weight of the totalpolymer component. Mathematically, this can be expressed as the weightof an ingredient divided by the total weight of the polymer, multipliedby a factor of 100.

As used herein, the term “substantially free” means less than about 5weight percent, preferably less than about 3 weight percent, morepreferably less than about 1 weight percent, and most preferably lessthan about 0.01 weight percent.

As used herein the term “resilience index” is defined as the differencein loss tangent measured at 10 cpm and 1000 cpm divided by 990 (thefrequency span) multiplied by 100,000 (for normalization and unitconvenience). The loss tangent is measured using an RPA 2000manufactured by Alpha Technologies of Akron, Ohio. The RPA 2000 is setto sweep from 2.5 to 1000 cpm at a temperature of 100° C. using an arcof 0.5 degrees. An average of six loss tangent measurements wereacquired at each frequency and the average is used in calculation of theresilience index. The computation of resilience index is as follows:

Resilience Index=100,000·[(loss tangent@10 cpm)−(loss tangent@11000cpm)]/990

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a golf ball 10 of the present invention includes acore 12 and a cover 14 surrounding the core 12. The core 12 preferablycomprises a center 16 and an outer core layer 18, and the cover 14comprises an outer cover layer 20 and an inner cover layer 22.

The golf ball cores of the present invention may comprise any of avariety of constructions. For example, the core of the golf ball maycomprise a conventional center surrounded by an intermediate mantle orouter core layer disposed between the center and the inner cover layer.The core may be a single layer or may comprise a plurality of layers.The innermost portion of the core may be solid or it may be a liquidfilled sphere. As with the core, the intermediate mantle or outer corelayer may also comprise a plurality of layers. The core may alsocomprise a solid or liquid filled center around which many yards of atensioned elastomeric material are wound.

The materials for solid cores include compositions having a base rubber,a crosslinking agent, a filler, and a co-crosslinking or initiatoragent. The base rubber typically includes natural or synthetic rubbers.A preferred base rubber is 1,4-polybutadiene having a cis-structure ofat least 40%. Most preferably, the base rubber compriseshigh-Mooney-viscosity rubber. If desired, the polybutadiene can also bemixed with other elastomers known in the art such as natural rubber,polyisoprene rubber and/or styrene-butadiene rubber in order to modifythe properties of the core.

The crosslinking agent includes a metal salt of an unsaturated fattyacid such as a zinc salt or a magnesium salt of an unsaturated fattyacid having 3 to 8 carbon atoms such as acrylic or methacrylic acid.Suitable cross linking agents include metal salt diacrylates,dimethacrylates and monomethacrylates wherein the metal is magnesium,calcium, zinc, aluminum, sodium, lithium or nickel.

One embodiment of the present invention relates to a multi-layer golfball having a core comprising a solid center surrounded by at least oneadditional solid outer core layer. At least one of the outer core layersis formed of a resilient rubber-based component comprising ahigh-Mooney-viscosity rubber, and a crosslinking agent present in anamount from about 20 to about 40 parts per hundred, from about 30 toabout 38 parts per hundred, and most preferably about 37 parts perhundred. It should be understood that the term “parts per hundred” iswith reference to the rubber by weight.

The center of the ball is preferably solid having a resilienthigh-Mooney-viscosity rubber component, and a crosslinking agent presentin an amount from about 15 to about 30 parts per hundred of the rubber,preferably in an amount from about 19 to about 25 parts per hundred ofthe rubber and most preferably having about 20 to 24 parts crosslinkingagent per hundred of rubber.

The initiator agent can be any known polymerization initiator whichdecomposes during the cure cycle. Suitable initiators include peroxidecompounds such as dicumyl peroxide, 1,1-di(t-butylperoxy)3,3,5-trimethyl cyclohexane, a-a bis(t-butylperoxy) diisopropylbenzene,2,5-dimethyl-2,5 di(t-butylperoxy) hexane or di-t-butyl peroxide andmixtures thereof.

As used herein, the term “filler” includes any compound or compositionthat can be used to vary the density and other properties of the core.Fillers typically include materials such as tungsten, zinc oxide, bariumsulfate, silica, calcium carbonate, zinc carbonate regrind (recycledcore material ground to 30 mesh particle), high-Mooney-viscosity rubberregrind, and the like.

The present invention also relates to multilayer golf balls having acore and a cover, such as a solid, hollow, or fluid-filled center, anouter core layer, and an inner and outer cover layer, disposed about thecenter. At least one of the center or intermediate layers includes areaction product that includes a cis-to-trans catalyst, a resilientpolymer component having polybutadiene, a free radical source, andoptionally, a crosslinking agent, a filler, or both.

The invention also includes a method to convert the cis-isomer of thepolybutadiene resilient polymer component to the trans-isomer during amolding cycle and to form a golf ball. Various combinations of polymers,cis-to-trans catalysts, fillers, crosslinkers, and a source of freeradicals, may be used. To obtain a higher resilience and lowercompression center or intermediate layer, a high-molecular weightpolybutadiene with a cis-isomer content preferably greater than about 90percent is converted to increase the percentage of trans-isomer contentat any point in the golf ball or portion thereof, preferably to increasethe percentage throughout substantially all of the golf ball or portionthereof, during the molding cycle. More preferably, thecis-polybutadiene isomer is present in an amount of greater than about95 percent of the total polybutadiene content. Without wishing to bebound by any particular theory, it is believed that a low amount of1,2-polybutadiene isomer (“vinyl-polybutadiene”) is desired in theinitial polybutadiene, and the reaction product. Typically, the vinylpolybutadiene isomer content is less than about 7 percent. Preferably,the vinyl polybutadiene isomer content is less than about 4 percent.More preferably, the vinyl polybutadiene isomer content is less thanabout 2 percent. Without wishing to be bound by any particular theory,it is also believed that the resulting mobility of the combined cis- andtrans-polybutadiene backbone is responsible for the lower modulus andhigher resilience of the reaction product and golf balls including thesame.

To produce a polymer reaction product that exhibits the higherresilience and lower modulus (low compression) properties that aredesirable and beneficial to golf ball playing characteristics,high-molecular-weight cis-1,4-polybutadiene, preferably may be convertedto the trans-isomer during the molding cycle. The polybutadiene materialtypically has a molecular weight of greater than about 200,000.Preferably, the polybutadiene molecular weight is greater than about250,000, more preferably between about 300,000 and 500,000. Withoutwishing to be bound by any particular theory, it is believed that thecis-to-trans catalyst component, in conjunction with the free radicalsource, acts to convert a percentage of the polybutadiene polymercomponent from the cis- to the trans-conformation. The cis-to-transconversion requires the presence of a cis-to-trans catalyst, such as anorganosulfur or metal-containing organosulfur compound, a substituted orunsubstituted aromatic organic compound that does not contain sulfur ormetal, an inorganic sulfide compound, an aromatic organometalliccompound, or mixtures thereof. The cis-to-trans catalyst component mayinclude one or more of the other cis-to-trans catalysts describedherein.

In one embodiment, the at least one organosulfur component issubstantially free of metal, which typically means less than about 10weight percent metal, preferably less than about 3 weight percent metal,more preferably less than about 1 weight percent metal, and mostpreferably only trace amounts of metal, such as less than about 0.01weight percent.

As used herein when referring to the invention, the term “organosulfurcompound(s)” or “organosulfur component(s),” means at least one of4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyldisulfide; bis(2-aminophenyl) disulfide; bis(4-aminophenyl) disulfide;bis(3-aminophenyl) disulfide; 2,2′-bis(4-aminonaphthyl) disulfide;2,2′-bis(3-aminonaphthyl) disulfide; 2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(5-aminonaphthyl) disulfide;2,2′-bis(6-aminonaphthyl) disulfide; 2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl) disulfide;1,1′-bis(2-aminonaphthyl) disulfide; 1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl) disulfide;1,1′-bis(4-aminonaphthyl) disulfide; 1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl) disulfide;1,1′-bis(7-aminonaphthyl) disulfide; 1,1′-bis(8-aminonaphthyl)disulfide; 1,2′-diamino-1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl) disulfide;bis(2-chlorophenyl) disulfide; bis(3-chlorophenyl) disulfide;bis(4-bromophenyl) disulfide; bis(2-bromophenyl) disulfide;bis(3-bromophenyl) disulfide; bis(4-fluorophenyl) disulfide;bis(4-iodophenyl) disulfide; bis(2,5-dichlorophenyl) disulfide;bis(3,5-dichlorophenyl) disulfide; bis(2,4-dichlorophenyl) disulfide;bis(2,6-dichlorophenyl) disulfide; bis(2,5-dibromophenyl) disulfide;bis(3,5-dibromophenyl) disulfide; bis(2-chloro-5-bromophenyl) disulfide;bis(2,4,6-trichlorophenyl) disulfide; bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl) disulfide; bis(2-cyanophenyl) disulfide;bis(4-nitrophenyl) disulfide; bis(2-nitrophenyl) disulfide;2,2′-dithiobenzoic acid ethylester; 2,2′-dithiobenzoic acid methylester;2,2′-dithiobenzoic acid; 4,4′-dithiobenzoic acid ethylester;bis(4-acetylphenyl) disulfide; bis(2-acetylphenyl) disulfide;bis(4-formylphenyl) disulfide; bis(4-carbamoylphenyl) disulfide;1,1′-dinaphthyl disulfide; 2,2′-dinaphthyl disulfide; 1,2′-dinaphthyldisulfide; 2,2′-bis(1-chlorodinaphthyl) disulfide;2,2′-bis(1-bromonaphthyl) disulfide; 1,1′-bis(2-chloronaphthyl)disulfide; 2,2′-bis(1-cyanonaphtyl) disulfide;2,2′-bis(1-acetylnaphthyl) disulfide; and the like; or a mixturethereof. Preferred organosulfur components include 4,4′-diphenyldisulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamido diphenyl disulfide,or a mixture thereof. A more preferred organosulfur component includes4,4′-ditolyl disulfide. The organosulfur cis-to-trans catalyst, whenpresent, is preferably present in an amount sufficient to produce thereaction product so as to contain at least about 12 percenttrans-polybutadiene isomer, but typically is greater than about 32percent trans-polybutadiene isomer based on the total resilient polymercomponent. Suitable metal-containing organosulfur components include,but are not limited to, cadmium, copper, lead, and tellurium analogs ofdiethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof. Suitable substituted orunsubstituted aromatic organic components that do not include sulfur ora metal include, but are not limited to, 4,4′-diphenyl acetylene,azobenzene, or a mixture thereof. The aromatic organic group preferablyranges in size from C₆ to C₂₀, and more preferably from C₆ to C₁₀.Suitable inorganic sulfide components include, but are not limited totitanium sulfide, manganese sulfide, and sulfide analogs of iron,calcium, cobalt, molybdenum, tungsten, copper, selenium, yttrium, zinc,tin, and bismuth. The cis-to-trans catalyst may also be a blend of anorganosulfur component and an inorganic sulfide component.

The cis-to-trans catalyst can also include a Group VIA component, asdefined herein. Elemental sulfur and polymeric sulfur are commerciallyavailable from, e.g., Elastochem, Inc. of Chardon, Ohio. Exemplarysulfur catalyst compounds include PB(RM-S)-80 elemental sulfur andPB(CRST)-65 polymeric sulfur, each of which is available fromElastochem, Inc. An exemplary tellurium catalyst under the tradenameTELLOY and an exemplary selenium catalyst under the tradename VANDEX areeach commercially available from RT Vanderbilt.

The cis-to-trans catalyst is preferably present in an amount from about0.1 to 10 parts per hundred of the total resilient polymer component.More preferably, the cis-to-trans catalyst is present in an amount fromabout 0.1 to 5 parts per hundred of the total resilient polymercomponent. Most preferably, the cis-to-trans catalyst is present in anamount from about 0.1 to 8 parts per hundred of the total resilientpolymer component. The cis-to-trans catalyst is typically present in anamount sufficient to produce the reaction product so as to increase thetrans-polybutadiene isomer content to contain from about 5 percent to 70percent trans-polybutadiene based on the total resilient polymercomponent.

The measurement of trans-isomer content of polybutadiene referred toherein was and can be accomplished as follows. Calibration standards areprepared using at least two polybutadiene rubber samples of knowntrans-content, e.g., high and low percent trans-polybutadiene). Thesesamples are used alone and blended together in such a way as to create aladder of trans-polybutadiene content of at least about 1.5% to 50% orto bracket the unknown amount, such that the resulting calibration curvecontains at least about 13 equally spaced points.

Using a commercially available Fourier Transform Infrared (“FTIR”)spectrometer equipped with a Photoacoustic (“PAS”) cell, a PAS spectrumof each standard was obtained using the following instrument parameters:scan at speed of 2.5 KHz (0.16 cm/s optical velocity), use a 1.2 KHzelectronic filter, set an undersampling ratio of 2 (number of lasersignal zero crossings before collecting a sample), co-add a minimum of128 scans at a resolution of 4 cm⁻¹ over a range of 375 to 4000 cm⁻¹with a sensitivity setting of 1.

The cis-, trans-, and vinyl-polybutadiene peaks are typically foundbetween 600 and 1100 cm-1 in the PAS spectrum. The area under each ofthe trans-polybutadiene peaks can be integrated. Determining thefraction of each peak area relative to the total area of the threeisomer peaks allow construction of a calibration curve of thetrans-polybutadiene area fraction versus the actual trans-polybutadienecontent. The correlation coefficient (R²) of the resulting calibrationcurve must be a minimum of 0.95. A PAS spectrum is obtained, using theparameters described above, for the unknown core material at the pointof interest (e.g., the surface or center of the core) by filling the PAScell with a sample containing a freshly cut, uncontaminated surface freeof foreign matters, such as mold release and the like. Thetrans-polybutadiene area fraction of the unknown is analyzed todetermine the actual trans-isomer content from the calibration curve.

In one known circumstance when barium sulfate is included, the abovemethod for testing trans-content may be less accurate. Thus, anadditional or alternative test of the trans-content of polybutadiene isas follows. Calibration standards are prepared using at least twopolybutadienes of known trans-content (e.g., high and low percenttrans-polybutadiene). These samples are used alone and blended togetherin such a way as to create a ladder of trans-polybutadiene content of atleast about 1.5% to 50% or to bracket the unknown amount, such that theresulting calibration curve contains at least about 13 equally spacedpoints.

Using a Fourier Transform Raman (“FT-Raman”) spectrometer equipped witha near-infrared laser, a Stokes Raman spectrum should be obtained fromeach standard using the following instrument parameters: sufficientlaser power to obtain a good signal-to-noise ratio (“S/N”) withoutcausing excessive heating or fluorescence (typically about 400 to 800 mWis suitable); a resolution of 2 cm⁻¹; over a Raman shift spectral rangeof about 400 to 4000 cm⁻¹; and co-adding at least 300 scans.

A calibration curve may be constructed from the data generated above,using a chemometrics approach and software such as PLSplus/IQ fromGalactic Industries Corp. of Salem, N.H. An acceptable calibration wasobtained with this software using a PLS-1 curve generated using an SNV(detrend) pathlength correction, a mean center data preparation, and a5-point SG second derivative over the spectral range from about 1600 to1700 cm⁻¹. The correlation coefficient (R2) of the resulting calibrationcurve must be a minimum of 0.95.

A Raman spectrum of the core material is obtained using this instrumentat the point of interest in the sample (e.g., surface or center of thegolf ball core). The sample must be free of foreign matter, such as moldrelease, etc. Analyze the spectrum of the sample using the PLScalibration curve to determine trans-polybutadiene isomer content of thesample.

A free-radical source, often alternatively referred to as a free-radicalinitiator, is required in the composition and method. The free-radicalsource is typically a peroxide, and preferably an organic peroxide.Suitable free-radical sources include di-t-amyl peroxide,di(2-t-butyl-peroxyisopropyl)benzene peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-t-butyl peroxide, 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxy)valerate, lauryl peroxide, benzoylperoxide, t-butyl hydroperoxide, and the like, and any mixture thereof.The peroxide is typically present in an amount greater than about 0.1parts per hundred of the total resilient polymer component, preferablyabout 0.1 to 15 parts per hundred of the resilient polymer component,and more preferably about 0.2 to 5 parts per hundred of the totalresilient polymer component. It should be understood by those ofordinary skill in the art that the presence of certain cis-to-transcatalysts according to the invention may require a larger amount offree-radical source, such as the amounts described herein, compared toconventional cross-linking reactions. The free radical source mayalternatively or additionally be one or more of an electron beam, UV orgamma radiation, x-rays, or any other high energy radiation sourcecapable of generating free radicals. It should be further understoodthat heat often facilitates initiation of the generation of freeradicals.

Crosslinkers are included to increase the hardness of the reactionproduct. Suitable crosslinking agents include one or more metallic saltsof unsaturated fatty acids or monocarboxylic acids, such as zinc,calcium, or magnesium acrylate salts, and the like, and mixturesthereof. Preferred acrylates include zinc acrylate, zinc diacrylate,zinc methacrylate, and zinc dimethacrylate, and mixtures thereof. Thecrosslinking agent must be present in an amount sufficient to crosslinka portion of the chains of polymers in the resilient polymer component.For example, the desired compression may be obtained by adjusting theamount of crosslinking. This may be achieved, for example, by alteringthe type and amount of crosslinking agent, a method well-known to thoseof ordinary skill in the art. The crosslinking agent is typicallypresent in an amount greater than about 0.1 percent of the resilientpolymer component, preferably from about 10 to 40 percent of theresilient polymer component, more preferably from about 10 to 30 percentof the resilient polymer component. When an organosulfur is selected asthe cis-to-trans catalyst, zinc diacrylate may be selected as thecrosslinking agent and is present in an amount of less than about 25phr.

Fillers added to one or more portions of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, the specific gravity (i.e., density-modifying fillers), themodulus, the tear strength, reinforcement, and the like. The fillers aregenerally inorganic, and suitable fillers include numerous metals ormetal oxides, such as zinc oxide and tin oxide, as well as bariumsulfate, zinc sulfate, calcium carbonate, barium carbonate, clay,tungsten, tungsten carbide, an array of silicas, and mixtures thereof.Fillers may also include various foaming agents or blowing agents whichmay be readily selected by one of ordinary skill in the art. Polymeric,ceramic, metal, and glass microspheres may be solid or hollow, andfilled or unfilled. Fillers are typically also added to one or moreportions of the golf ball to modify the density thereof to conform touniform golf ball standards. Fillers may also be used to modify theweight of the center or at least one additional layer for specialtyballs, e.g., a lower weight ball is preferred for a player having a lowswing speed.

The polymers, free-radical initiator, filler(s), and any other materialsused in forming either the golf ball center or any portion of the core,in accordance with invention, may be combined to form a mixture by anytype of mixing known to one of ordinary skill in the alt. Suitable typesof mixing include single pass and multi-pass mixing, and the like. Thecrosslinking agent, and any other optional additives used to modify thecharacteristics of the golf ball center or additional layer(s), maysimilarly be combined by any type of mixing. A single-pass mixingprocess where ingredients are added sequentially is preferred, as thistype of mixing tends to increase efficiency and reduce costs for theprocess. The preferred mixing cycle is single step wherein the polymer,cis-trans catalyst, filler, zinc diacrylate, and peroxide are addedsequentially. Suitable mixing equipment is well known to those ofordinary skill in the art, and such equipment may include a Banburymixer, a two-roll mill, or a twin screw extruder. Conventional mixingspeeds for combining polymers are typically used, although the speedmust be high enough to impart substantially uniform dispersion of theconstituents. On the other hand, the speed should not be too high, ashigh mixing speeds tend to break down the polymers being mixed andparticularly may undesirably decrease the molecular weight of theresilient polymer component. The speed should thus be low enough toavoid high shear, which may result in loss of desirably high molecularweight portions of the polymer component. Also, too high a mixing speedmay undesirably result in creation of enough heat to initiate thecrosslinking before the preforms are shaped and assembled around a core.The mixing temperature depends upon the type of polymer components, andmore importantly, on the type of free-radical initiator. For example,when using di(2-t-butyl-peroxyisopropyl)benzene as the free-radicalinitiator, a mixing temperature of about 80° C. to 125° C., preferablyabout 88° C. to 110° C., and more preferably about 90° C. to 100° C., issuitable to safely mix the ingredients. Additionally, it is important tomaintain a mixing temperature below the peroxide decompositiontemperature. For example, if dicumyl peroxide is selected as theperoxide, the temperature should not exceed 200° F. Suitable mixingspeeds and temperatures are well-known to those of ordinary skill in theart, or may be readily determined without undue experimentation.

The mixture can be subjected to, e.g., a compression or injectionmolding process, to obtain solid spheres for the center or hemisphericalshells for forming an intermediate layer. The polymer mixture issubjected to a molding cycle in which heat and pressure are appliedwhile the mixture is confined within a mold. The cavity shape depends onthe portion of the golf ball being formed. The compression and heatliberates free radicals by decomposing one or more peroxides, which mayinitiate the cis-to-trans conversion and crosslinking simultaneously.The temperature and duration of the molding cycle are selected basedupon the type of peroxide and cis-trans catalyst selected. The moldingcycle may have a single step of molding the mixture at a singletemperature for a fixed time duration. An example of a single stepmolding cycle, for a mixture that contains dicumyl peroxide, would holdthe polymer mixture at 340° F. for a duration of 15 minutes. The moldingcycle may also include a two-step process, in which the polymer mixtureis held in the mold at an initial temperature for an initial duration oftime, followed by holding at a second, typically higher temperature fora second duration of time. An example of a two-step molding cycle wouldbe holding the mold at 290° F. for 40 minutes, then ramping the mold to340° F. where it is held for a duration of 20 minutes. In a preferredembodiment of the current invention, a single-step cure cycle isemployed. Single-step processes are effective and efficient, reducingthe time and cost of a two-step process. The resilient polymercomponent, polybutadiene, cis-to-trans conversion catalyst, additionalpolymers, free-radical initiator, filler, and any other materials usedin forming either the golf ball center or any portion of the core, inaccordance with the invention, may be combined to form a golf ball by aninjection molding process, which is also well-known to one of ordinaryskill in the art. Although the curing time depends on the variousmaterials selected, a particularly suitable curing time is about 5 to 18minutes, preferably from about 8 to 15 minutes, and more preferably fromabout 10 to 12 minutes. Those of ordinary skill in the art will bereadily able to adjust the curing time upward or downward based on theparticular materials used and the discussion herein.

The cured resilient polymer component, which contains a greater amountof trans-polybutadiene than the uncured resilient polymer component, isformed into an article having a first hardness at a point in theinterior and a surface having a second hardness such that the secondhardness differs from the first hardness by greater than 10 percent ofthe first hardness. Preferably, the article is a sphere and the point isthe midpoint of the article. In another embodiment, the second hardnessdiffers from the first by greater than 20 percent of the first hardness.The cured article also has a first amount of trans-polybutadiene at aninterior location and a second amount of trans-polybutadiene at asurface location, wherein the first amount is at least about 6 percentless than the second amount, preferably at least about 10 percent lessthan the second amount, and more preferably at least about 20 percentless than the second amount. The interior location is preferably amidpoint and the article is preferably a sphere. The compression of thecore, or portion of the core, of golf balls prepared according to theinvention is preferably below about 50, more preferably below about 25.

The cover provides the interface between the ball and a club. Propertiesthat are desirable for the cover are good moldability, high abrasionresistance, high tear strength, high resilience, and good mold release,among others. The cover typically has a thickness to provide sufficientstrength, good performance characteristics and durability. The coverpreferably has a thickness of less than about 0.1 in, more preferably,less than about 0.05 in, and most preferably, between about 0.02 andabout 0.04 in. The invention is particularly directed towards amultilayer golf ball which comprises a core, an inner cover layer, andan outer cover layer. In this embodiment, preferably, at least one ofthe inner and outer cover layers has a thickness of less than about 0.05in, more preferably between about 0.02 in and about 0.04 in. Mostpreferably, the thickness of either layer is about 0.03 in.

When the golf ball of the present invention includes an intermediatelayer, such as an inner cover layer, this layer can include anymaterials known to those of ordinary skill in the art, includingthemoplastic and thermosetting materials, but preferably theintermediate layer can include any suitable materials, such as ioniccopolymers of ethylene and an unsaturated monocarboxylic acid which areavailable under the trademark SURLYN of E.I. DuPont de Nemours & Co., ofWilmington, Del., or IOTEK or ESCOR of Exxon. These are copolymers orterpolymers of ethylene and methacrylic acid or acrylic acid partiallyneutralized with salts of zinc, sodium, lithium, magnesium, potassium,calcium, manganese, nickel or the like, in which the salts are thereaction product of an olefin having from 2 to 8 carbon atoms and anunsaturated monocarboxylic acid having 3 to 8 carbon atoms. Thecarboxylic acid groups of the copolymer may be totally or partiallyneutralized and might include methacrylic, crotonic, maleic, fumaric oritaconic acid.

This golf ball can likewise include one or more homopolymeric orcopolymeric inner cover layer materials, such as:

(1) Vinyl resins, such as those formed by the polymerization of vinylchloride, or by the copolymerization of vinyl chloride with vinylacetate, acrylic esters or vinylidene chloride;

(2) Polyolefins, such as polyethylene, polypropylene, polybutylene andcopolymers such as ethylene methylacrylate, ethylene ethylacrylate,ethylene vinyl acetate, ethylene methacrylic or ethylene acrylic acid orpropylene acrylic acid and copolymers and homopolymers produced using asingle-site catalyst or a metallocene catalyst;

(3) Polyurethanes, such as those prepared from polyols and diisocyanatesor polyisocyanates and those disclosed in U.S. Pat. No. 5,334,673;

(4) Polyureas, such as those disclosed in U.S. Pat. No. 5,484,870;

(5) Polyamides, such as poly(hexamethylene adipamide) and othersprepared from diamines and dibasic acids, as well as those from aminoacids such as poly(caprolactam), and blends of polyamides with SURLYN,polyethylene, ethylene copolymers, ethyl-propylene-non-conjugated dieneterpolymer, and the like;

(6) Acrylic resins and blends of these resins with poly vinyl chloride,elastomers, and the like;

(7) Thermoplastics, such as urethanes; olefinic thermoplastic rubbers,such as blends of polyolefins with ethylene-propylene-non-conjugateddiene terpolymer; block copolymers of styrene and butadiene, isoprene orethylene-butylene rubber; or copoly(ether-amide), such as PEBAX, sold byELF Atochem of Philadelphia, Pa.;

(8) Polyphenylene oxide resins or blends of polyphenylene oxide withhigh impact polystyrene as sold under the trademark NORYL by GeneralElectric Company of Pittsfield, Mass.;

(9) Thermoplastic polyesters, such as polyethylene terephthalate,polybutylene terephthalate, polyethylene terephthalate/glycol modifiedand elastomers sold under the trademarks HYTREL by E.I. DuPont deNemours & Co. of Wilmington, Del., and LOMOD by General Electric Companyof Pittsfield, Mass.;

(10) Blends and alloys, including polycarbonate with acrylonitrilebutadiene styrene, polybutylene terephthalate, polyethyleneterephthalate, styrene maleic anhydride, polyethylene, elastomers, andthe like, and polyvinyl chloride with acrylonitrile butadiene styrene orethylene vinyl acetate or other elastomers; and

(11) Blends of thermoplastic rubbers with polyethylene, propylene,polyacetal, nylon, polyesters, cellulose esters, and the like.

Preferably, the optional intermediate layer includes polymers, such asethylene, propylene, butene-1 or hexane-1 based homopolymers orcopolymers including functional monomers, such as acrylic andmethacrylic acid and fully or partially neutralized ionomer resins andtheir blends, methyl acrylate, methyl methacrylate homopolymers andcopolymers, imidized, amino group containing polymers, polycarbonate,reinforced polyamides, polyphenylene oxide, high impact polystyrene,polyether ketone, polysulfone, poly(phenylene sulfide),acrylonitrile-butadiene, acrylic-styrene-acrylonitrile, poly(ethyleneterephthalate), poly(butylene terephthalate), poly(ethelyne vinylalcohol), poly(tetrafluoroethylene) and their copolymers includingfunctional comonomers, and blends thereof. Suitable cover compositionsalso include a polyether or polyester thermoplastic urethane, athermoset polyurethane, a low modulus ionomer, such as acid-containingethylene copolymer ionomers, including E/X/Y terpolymers where E isethylene, X is an acrylate or methacrylate-based softening comonomerpresent in about 0 to 50 weight percent and Y is acrylic or methacrylicacid present in about 5 to 35 weight percent. More preferably, in a lowspin rate embodiment designed for maximum distance, the acrylic ormethacrylic acid is present in about 16 to 35 weight percent, making theionomer a high modulus ionomer. In a higher spin embodiment, the innercover layer includes an ionomer where an acid is present in about 10 to15 weight percent and includes a softening comonomer.

The cover preferably include a polyurethane composition comprising thereaction product of at least one polyisocyanate, polyol, and at leastone curing agent.

Any polyisocyanate available to one of ordinary skill in the art issuitable for use according to the invention. Exemplary polyisocyanatesinclude, but are not limited to, 4,4′-diphenylmethane diisocyanate(“MDI”), polymeric MDI, carbodiimide-modified liquid MDI,4,4′-dicyclohexylmethane diisocyanate (“H₁₂MDI”), p-phenylenediisocyanate (“PPDI”), toluene diisocyanate (“TDI”),3,3′-dimethyl-4,4′-biphenylene diisocyanate (“TODI”),isophoronediisocyanate (“IPDI”), hexamethylene diisocyanate (“HDI”),naphthalene diisocyanate (“NDI”); xylene diisocyanate (“XDI”);para-tetramethylxylene diisocyanate (“p-TMXDI”); meta-tetramethylxylenediisocyanate (“m-TMXDI”); ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; cyclohexyldiisocyanate; 1,6-hexamethylene-diisocyanate (“HDI”);dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of2,4,4-trimethyl-1,6-hexane diisocyanate (“TMDI”), tetracenediisocyanate, napthalene diisocyanate, anthracene diisocyanate, andmixtures thereof. Polyisocyanates are known to those of ordinary skillin the art as having more than one isocyanate group, e.g., di-, tri- andtetra-isocyanate. Preferably, the polyisocyanate includes MDI, PPDI,TDI, or a mixture thereof, and more preferably, the polyisocyanateincludes MDI. It should be understood that, as used herein, the term“MDI” includes 4,4′-diphenylmethane diisocyanate, polymeric MDI,carbodiimide-modified liquid MDI, and mixtures thereof and,additionally, that the diisocyanate employed may be “low free monomer,”understood by one of ordinary skill in the art to have lower levels of“free” monomer isocyanate groups, typically less than about 0.1% freemonomer groups. Examples of “low free monomer” diisocyanates include,but are not limited to Low Free Monomer MDI, Low Free Monomer TDI, andLow Free Monomer PPDI.

The at least one polyisocyanate should have less than about 14%unreacted NCO groups. Preferably, the at least one polyisocyanate has nogreater than about 7.5% NCO, and more preferably, less than about 7.0%.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polyeaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (“PTMEG”),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

In another embodiment, polyester polyols are included in thepolyurethane material of the invention. Suitable polyester polyolsinclude, but are not limited to, polyethylene adipate glycol,polybutylene adipate glycol, polyethylene propylene adipate glycol,ortho-phthalate-1,6-hexanediol, and mixtures thereof. The hydrocarbonchain can have saturated or unsaturated bonds, or substituted orunsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in thematerials of the invention. Suitable polyeaprolactone polyols include,but are not limited to, 1,6-hexanediol-initiated polycaprolactone,diethylene glycol initiated polycaprolactone, trimethylol propaneinitiated polycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, the polycarbonate polyols are included in thepolyurethane material of the invention. Suitable polycarbonates include,but are not limited to, polyphthalate carbonate. The hydrocarbon chaincan have saturated or unsaturated bonds, or substituted or unsubstitutedaromatic and cyclic groups. In one embodiment, the molecular weight ofthe polyol is from about 200 to about 4000.

Polyamine curatives are also suitable for use in the polyurethanecomposition of the invention and have been found to improve cut, shear,and impact resistance of the resultant balls. Preferred polyaminecuratives include, but are not limited to,3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenylmethane; p,p′-methylene dianiline (“MDA”); m-phenylenediamine (“MPDA”);4,4′-methylene-bis-(2-chloroaniline) (“MOCA”);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trim ethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof, such as ETHACURE 300, commercially available fromAlbermarle Corporation of Baton Rouge, La. Suitable polyamine curatives,which include both primary and secondary amines, preferably havemolecular weights ranging from about 64 to about 2000.

At least one of a diol, triol, tetraol, or hydroxy-terminated curativesmay be added to the aforementioned polyurethane composition. Suitablediol, triol, and tetraol groups include ethylene glycol; diethyleneglycol; polyethylene glycol; propylene glycol; polypropylene glycol;lower molecular weight polytetramethylene ether glycol;1,3-bis(2-hydroxyethoxy) benzene; 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy} benzene;1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol;resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl)ether; and mixtures thereof. Preferredhydroxy-terminated curatives include ethylene glycol; diethylene glycol;1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol, trimethylol propane,and mixtures thereof. Preferably, the hydroxy-terminated curatives havemolecular weights ranging from about 48 to 2000. It should be understoodthat molecular weight, as used herein, is the absolute weight averagemolecular weight and would be understood as such by one of ordinaryskill in the art.

Both the hydroxy-terminated and amine curatives can include one or moresaturated, unsaturated, aromatic, and cyclic groups. Additionally, thehydroxy-terminated and amine curatives can include one or more halogengroups. The polyurethane composition can be formed with a blend ormixture of curing agents. If desired, however, the polyurethanecomposition may be formed with a single curing agent.

Any method known to one of ordinary skill in the art may be used tocombine the polyisocyanate, polyol, and curing agent of the presentinvention. One commonly employed method, known in the art as a one-shotmethod, involves concurrent mixing of the polyisocyanate, polyol, andcuring agent. This method results in a mixture that is inhomogenous(more random) and affords the manufacturer less control over themolecular structure of the resultant composition. A preferred method ofmixing is known as a prepolymer method. In this method, thepolyisocyanate and the polyol are mixed separately prior to addition ofthe curing agent. This method affords a more homogeneous mixtureresulting in a more consistent polymer composition.

An optional filler component may be chosen to impart additional densityto blends of the previously described components. The selection of suchfiller(s) is dependent upon the type of golf ball desired (i.e.,one-piece, two-piece multi-component, or wound). Examples of usefulfillers include zinc oxide, barium sulfate, calcium oxide, calciumcarbonate and silica, as well as the other well known correspondingsalts and oxides thereof. Additives, such as nanoparticles, glassspheres, and various metals, such as titanium and tungsten, can be addedto the polyurethane compositions of the present invention, in amounts asneeded, for their well-known purposes. Additional components which canbe added to the polyurethane composition include UV stabilizers andother dyes, as well as optical brighteners and fluorescent pigments anddyes. Such additional ingredients may be added in any amounts that willachieve their desired purpose. Due to the very thin nature, it has beenfound by the present invention that the use of a castable, reactivematerial, which is applied in a fluid form, makes it possible to obtainvery thin outer cover layers on golf balls. Specifically, it has beenfound that castable, reactive liquids, which react to form a urethaneelastomer material, provide desirable very thin outer cover layers.

The castable, reactive liquid employed to form the urethane elastomermaterial can be applied over the inner core using a variety ofapplication techniques such as spraying, dipping, spin coating, or flowcoating methods which are well known in the art. An example of asuitable coating technique is that which is disclosed in U.S. Pat. No.5,733,428, filed May 2, 1995 entitled “Method And Apparatus For FormingPolyurethane Cover On A Golf Ball”, the disclosure of which is herebyincorporated by reference in its entirety in the present application.

The cover is preferably formed around the inner cover layer by mixingand introducing the material in the mold halves. It is important thatthe viscosity be measured over time, so that the subsequent steps offilling each mold half, introducing the core into one half and closingthe mold can be properly timed for accomplishing centering of the corecover halves fusion and achieving overall uniformity. Suitable viscosityrange of the curing urethane mix for introducing cores into the moldhalves is determined to be approximately between about 2,000 cP andabout 30,000 cP, with the preferred range of about 8,000 cP to about15,000 cP.

To start the cover formation, mixing of the prepolymer and curative isaccomplished in motorized mixer including mixing head by feeding throughlines metered amounts of curative and prepolymer. Top preheated moldhalves are filled and placed in fixture units using pins moving intoholes in each mold. After the reacting materials have resided in topmold halves for about 40 to about 80 seconds, a core is lowered at acontrolled speed into the gelling reacting mixture. At a later time, abottom mold half or a series of bottom mold halves have similar mixtureamounts introduced into the cavity.

A ball cup holds the ball core through reduced pressure (or partialvacuum) in hose. Upon location of the coated core in the halves of themold after gelling for about 40 to about 80 seconds, the vacuum isreleased allowing core to be released. The mold halves, with core andsolidified cover half thereon, are removed from the centering fixtureunit, inverted and mated with other mold halves which, at an appropriatetime earlier, have had a selected quantity of reacting polyurethaneprepolymer and curing agent introduced therein to commence gelling.

Similarly, U.S. Pat. No. 5,006,297 to Brown et al. and U.S. Pat. No.5,334,673 to Wu both also disclose suitable molding techniques which maybe utilized to apply the castable reactive liquids employed in thepresent invention. Further, U.S. Pat. Nos. 6,180,040 and 6,180,722disclose methods of preparing dual core golf balls. The disclosures ofthese patents are hereby incorporated by reference in their entirety.However, the method of the invention is not limited to the use of thesetechniques.

Depending on the desired properties, balls prepared according to theinvention can exhibit substantially the same or higher resilience, orcoefficient of restitution (“COR”), with a decrease in compression ormodulus, compared to balls of conventional construction. Additionally,balls prepared according to the invention can also exhibit substantiallyhigher resilience, or COR, without an increase in compression, comparedto balls of conventional construction. Another measure of thisresilience is the “loss tangent,” or tan δ, which is obtained whenmeasuring the dynamic stiffness of an object. Loss tangent andterminology relating to such dynamic properties is typically describedaccording to ASTM D4092-90. Thus, a lower loss tangent indicates ahigher resiliency, thereby indicating a higher rebound capacity. Lowloss tangent indicates that most of the energy imparted to a golf ballfrom the club is converted to dynamic energy, i.e., launch velocity andresulting longer distance. The rigidity or compressive stiffness of agolf ball may be measured, for example, by the dynamic stiffness. Ahigher dynamic stiffness indicates a higher compressive stiffness. Toproduce golf balls having a desirable compressive stiffness, the dynamicstiffness of the crosslinked reaction product material should be lessthan about 50,000 N/m at −50° C. Preferably, the dynamic stiffnessshould be between about 10,000 and 40,000 N/m at −50° C., morepreferably, the dynamic stiffness should be between about 20,000 and30,000 N/m at −50° C.

The resultant golf balls typically have a coefficient of restitution ofgreater than about 0.7, preferably greater than about 0.75, and morepreferably greater than about 0.78. The golf balls also typically havean Atti compression of at least about 40, preferably from about 50 to120, and more preferably from about 60 to 100. The golf ballpolybutadiene material of the present invention typically has a flexuralmodulus of from about 500 psi to 300,000 psi, preferably from about 2000to 200,000 psi. The golf ball polybutadiene material typically has ahardness of at least about 15 Shore A, preferably between about 30 ShoreA and 80 Shore D, more preferably between about 50 Shore A and 60 ShoreD.

The specific gravity of the center composition is typically greater thanabout 0.7 and preferably greater than about 1.0. The center and theouter core layer may have the same or different specific gravity values.In one embodiment, the center and outer core layer have differentspecific gravity values. It is preferred, however, that the specificgravity of the outer core layer and the center differ by less than 0.1.

The center composition should comprise at least one rubber materialhaving a resilience index of at least about 40. Preferably theresilience index is at least about 50. Polymers that produce resilientgolf balls and, therefore, are suitable for the present invention,include but are not limited to CB23, CB22, BR60, and 1207G. To clarifythe method of computation for resilience index, the resilience index forCB23, for example, is computed as follows:

Resilience Index for CB23=100,000·[(0.954)−(0.407)]/990 Resilience Indexfor CB23=55

The molding process and composition of golf ball portions typicallyresults in a gradient of material properties. Methods employed in theprior art generally exploit hardness to quantify these gradients.Hardness is a qualitative measure of static modulus and does notrepresent the modulus of the material at the deformation ratesassociated with golf ball use, i.e., impact by a club. As is well knownto one skilled in the art of polymer science, the time-temperaturesuperposition principle may be used to emulate alternative deformationrates. For golf ball portions including polybutadiene, a 1-Hzoscillation at temperatures between 0° C. and −50° C. are believed to bequalitatively equivalent to golf ball impact rates. Therefore,measurement of loss tangent and dynamic stiffness at 0° C. to −50° C.may be used to accurately anticipate golf ball performance, preferablyat temperatures between about −20° C. and −50° C.

Additionally, the unvulcanized rubber, such as polybutadiene, in golfballs prepared according to the invention typically has a Mooneyviscosity of between about 40 and about 80, more preferably, betweenabout 45 and about 60, and most preferably, between about 45 and about55. Mooney viscosity is typically measured according to ASTM D-1646.

When golf balls are prepared according to the invention, they typicallywill have dimple coverage greater than about 60 percent, preferablygreater than about 65 percent, and more preferably greater than about 75percent. The flexural modulus of the cover on the golf balls, asmeasured by ASTM method D6272-98, Procedure B, is typically greater thanabout 500 psi, and is preferably from about 500 psi to 150,000 psi. Asdiscussed herein, the outer cover layer is preferably formed from arelatively soft polyurethane material. In particular, the material ofthe outer cover layer should have a material hardness, as measured byASTM-2240, preferably less than about 60 Shore D, more preferably lessthan about 55 Shore D, and most preferably less than about 50 Shore D.The outer cover layer hardness, as measured on the golf ball, ispreferably greater than about 50. The inner cover layer preferably has amaterial hardness less than 72 Shore D, more preferably less than about70 Shore D, and most preferably, less than about 68 Shore D. It ispreferred that the center, outer core layer, and inner cover layer eachhave a different hardness and more preferably, that the hardnessprogressively increases away from the center until reaching the outercover layer, i.e., the outer core layer is harder than the center andthe inner cover layer is harder than the outer core layer.

The overall outer diameter (“OD”) of the center is preferably from about0.375 in to about 1.4 in, more preferably from about 0.5 in to about1.25 in, and most preferably from about 0.9 in to about 1.2 in. The ODof the outer core layer is preferably from about 1.4 in to about 1.62in, more preferably from about 1.52 in to about 1.59 in, and mostpreferably from about 1.535 in to about 1.58 in. The OD of the innercover layer of the golf balls of the present invention is preferablygreater than about 1.58 in, more preferably from about 1.59 in to about1.66 in, and most preferably from about 1.6 in to about 1.64 in.

The present multilayer golf ball can have an overall diameter of anysize. Although the United States Golf Association (“USGA”)specifications limit the minimum size of a competition golf ball to1.680 in. There is no specification as to the maximum diameter. Golfballs of any size, however, can be used for recreational play. Thepreferred diameter of the present golf balls is from about 1.680 in toabout 1.800 in. The more preferred diameter is from about 1.680 in toabout 1.760 in. The most preferred diameter is about 1.680 in to about1.740 in.

The golf balls of the present invention should have a moment of inertia(“MOI”) of less than about 83 and, preferably, less than about 82. TheMOI is typically measured on model number MOI-005-104 Moment of InertiaInstrument manufactured by Inertia Dynamics of Collinsville, Conn. Theinstrument is plugged into a PC for communication via a COMM port and isdriven by MOI Instrument Software version #1.2.

The golf balls of the present invention should have a center deflectionof greater than about 4.5 mm under a load of 100 Kg. Preferably, thecenter deflection is greater than about 4.8 mm and, more preferably,about 5.0 mm under a load of 100 Kg. The deflection data is measuredwith a Stable Micro Systems, Materials Master, (model number MT-LQ)instrument commercially available from Mono Research Labs. The MT-LQ isequipped with a 500 Kg load cell, which begins measuring deflection when60 g is placed on it.

Prior to measuring deflection, the platens are calibrated. Aftercalibration, the operator places the sphere to be measured on thesurface of the bottom platen. The top platen moves down with a crossheadspeed of one in/min. When the surface of the top platen contacts thesphere and reaches a compressive force of 60 g (the trigger force), thedisplacement is measured as a function of force, with force being theindependent variable on the x axis. The instrument measures apredetermined number of data points/min which result in a plot ofdisplacement versus force, from which the displacement of the sphere ata load of 100 Kg can be determined.

Example

Two golf balls were prepared according to the present invention and aredesignated VDC45 and VDC48 in Table I below. The VDC golf ballscontained a core formed of a 1.0-in-diameter solid center and an outercore layer having a thickness of 0.275 in to form a core having an outerdiameter of 1.55 in. The core was surrounded by an inner cover layerhaving a thickness of 0.035 in and an outer cover layer having athickness of 0.030 in, to provide a golf ball outer diameter of 1.68 in.A control golf ball was prepared according to conventional technology.The control ball was formed of a solid core having a diameter of 1.550in, an inner cover layer having a thickness of 0.035 in, and an outercover layer having a thickness of 0.030 in, to provide a golf ball outerdiameter of 1.68 in. The center compositions for both golf balls arepresented below in Table I.

TABLE I Center Composition VDC45 VDC48 Control CB23 100.0 100.0 100.0zinc diacrylate 25.05 25.05 27.0 zinc oxide 5.26 5.26 4.3 di-tolyldisulfide 0.63 0.63 — DCP-70¹ 2.0 2.0 — tungsten 33.4 33.4 12.74 colordispersion 0.07 0.07 0.14 Trigonox-265² — — 0.53 ¹DCP-70 is dicumylperoxide on a binder in pellet and is commercially available fromElastochem, Inc. of Chardon, OH ²a peroxide mixture on fillercommercially available from Akzo Nobel Chemicals Inc. of Chicago, IL

The outer core layer composition for both VDC balls compriseshigh-Mooney-viscosity CB23 polybutadiene, zinc diacrylate, zinc oxide,DCP-70, Kurary TP 251, Varox 231XL, and a color dispersion. The innercover layers were the same construction for both VDC balls and thecontrol ball. The inner cover layers were formed of a 50/50 Na/Li blendof SURLYN® 8945 and SURLYN® 7940. The outer cover layer of the VDC45ball comprises a PMS1088 prepolymer, commercially available fromPolyurethane Specialties Co. (77.8%) cured with Ethacure 300,commercially available from Albemarle Corp. (18.7%), and whitedispersion, commercially available from Harwich Chemical (3.5%).

The outer cover layer of the VDC48 ball comprises a Vibrathane B-625prepolymer, commercially available from Uniroyal (80.5%; NCO level:6.1-6.6%) cured with Ethacure 300, commercially available from AlbemarleCorp. (16%), and white dispersion, commercially available from HarwichChemical (3.5%).

The VDC balls were formed in two different constructions, one with anouter cover layer having a material Shore D hardness of about 45, and asecond with an outer cover layer having a material Shore D hardness ofabout 48. The VCD balls were tested for a variety of golf ballproperties, such as ball compression, center hardness (interior andsurface), core layer hardness, inner cover layer hardness, coverhardness, and compared to the Control ball, also tested for the sameproperties.

TABLE II Ball Properties VDC45 VDC48 Control Ball Compression (Atti) 9696 85 Center - surface hardness¹ (Shore C) 73.3 73.3 Outer Core Layerhardness¹ (Shore C) 83.3 83.3 Inner Cover Layer hardness¹ (Shore D) 62.862.8 Cover hardness¹ (Shore D) 56 58 57 moment of inertia (g · cm²)80.73 80.73 81.11 CoR 0.815 0.817 0.815 ¹hardness measured directly onthe golf ball (as compared to material hardness)

The launch angle and spin were measured for both VDC balls and theControl ball, for a variety of golf clubs. The data for each ball, offof each club type, are presented below in Table III.

TABLE III Launch Angle (°) Spin (rpm) Club: Pro Driver¹ VDC45 9.5 3072VDC48 9.3 3134 Control 9.2 3357 Club: Standard Driver² VDC45 9.1 3091VDC48 9.1 3038 Control 9.0 3370 Club: 8-Iron³ VDC45 19.3 7035 VDC48 19.66863 Control 18.9 7457 Club: Wedge⁴ VDC45 25.5 9335 VDC48 25.5 9290Control 25.0 9623 ¹Ball Speed: 167; Launch Angle: 9°; Spin Rate: 3500rpm; Club: Driver; Club Head: 975D; Loft: 7.5°; Shaft: Graphite DesignYS9-X ²Ball Speed: 160 mph; Launch Angle: 9.5°; Spin Rate: 3000 rpm;Club: Driver; Club Head: 975D; Loft: 8.5°; Shaft: X100 ³Ball Speed: 115mph; Launch Angle: 18.5°; Spin Rate: 9000 rpm; Club: 8-iron; Club Head:DCI Black; Loft: 40°; Shaft: X100 ⁴Ball Speed: 95; Launch Angle: 24°;Spin Rate: 10400 rpm; Club: wedge; Club Head: DCI Black; Loft: 46°;Shaft: X-100

It is clear from the data presented in Table III, that the golf ball ofthe present invention decreases driver spin for both a Pro driver and aStandard driver. One of ordinary skill in the art is well aware thatdecreasing driver spin to optimize flight increases distance off thetee. Too much 8-iron spin can make approach shots into the greendifficult to control whereas wedge spin is important to making approachshots stop at desired locations on the green, especially when a playeris pitching or chipping to the green.

The invention described and claimed herein is not to be limited in scopeby the specific embodiments herein disclosed, since these embodimentsare intended as illustrations of several aspects of the invention. Anyequivalent embodiments are intended to be within the scope of thisinvention. Indeed, various modifications of the invention in addition tothose shown and described herein will become apparent to those skilledin the art from the foregoing description. Such modifications are alsointended to fall within the scope of the appended claims.

1. A golf ball comprising: a core comprising an inner core and at leastone outer core layer disposed about the inner core, at least one of theinner core or the outer core layer comprising a surface amount oftrans-polybutadiene and an interior amount of trans-polybutadiene atleast 6 percent less than the surface amount; and a cover comprising aninner cover layer and an outer cover layer, the inner cover layercomprising a block copolymer of styrene and butadiene, isoprene, orethylene-butylene rubber and having a material hardness of about 60 to70 Shore D; and the outer cover layer comprising a castable polyurethaneor polyurea and having a material hardness of 55 Shore D or less;wherein the inner core has an interior hardness and a surface hardnessdiffering from the interior hardness by greater than 20 percent.
 2. Thegolf ball of claim 1, wherein the outer cover material hardness is 50Shore D or less.
 3. The golf ball of claim 1, wherein the inner coverlayer outer diameter is from 1.59 inches to 1.66 inches.
 4. The golfball of claim 3, wherein the inner cover layer outer diameter is from1.6 inches to 1.64 inches.
 5. The golf ball of claim 1, wherein theinner core has an outer diameter of about 0.5 inches to 1.25 inches. 6.The golf ball of claim 5, wherein the inner core outer diameter is about0.9 inches to 1.2 inches.
 7. The golf ball of claim 1, wherein the outercore layer has an outer diameter of about 1.52 inches to 1.59 inches. 8.The golf ball of claim 7, wherein the outer core layer outer diameter isabout 1.535 inches to 1.58 inches.
 9. A golf ball comprising: a corecomprising an inner core and at least one outer core layer disposedabout the inner core, at least one of the inner core or outer core layercomprises a thermosetting rubber composition comprising atrans-polybutadiene infrared peak between 600 cm⁻¹ and 1100 cm⁻¹ suchthat an area under the trans-polybutadiene infrared peak is at least 5to 70 percent of a total area of cis-, trans-, and vinyl-polybutadieneinfrared peaks; and a cover comprising an inner cover layer and an outercover layer, the inner cover layer comprising a thermosetting orthermoplastic material and having a material hardness of about 60 to 70Shore D; and the outer cover layer comprising a castable polyurethane orpolyurea material and having a material hardness of 55 Shore D or less.10. The golf ball of claim 1, wherein the inner core is solid.